Magnox
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2008-07-11T23:39:02Z
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/* External links */ Add IAEA paper
[[Image:Magnox reactor schematic.svg|thumb|310px|Schematic diagram of a Magnox nuclear reactor showing gas flow. Note that the heat exchanger is outside the concrete radiation shielding. This represents an early Magnox design with a cylindrical, steel, pressure vessel.]]
:''For other uses of the term see [[Magnox (disambiguation)]].''
'''Magnox''' is a now obsolete type of [[nuclear reactor|nuclear power reactor]] which was designed and is still in use in the United Kingdom, and was exported to other countries, both as a power plant, and, when operated accordingly, as a producer of [[plutonium]] for [[nuclear weapons]]. The name '''magnox''' comes from the [[Magnox (alloy)|alloy]] used to clad the fuel rods inside the reactor.
==General description==
Magnox reactors are pressurised, [[carbon dioxide]] cooled, [[Nuclear graphite|graphite]] [[neutron moderator|moderated]] reactors using [[natural uranium]] (i.e. unenriched) as fuel and magnox alloy as fuel cladding. [[Boron]]-steel control rods were used. The design was continuously refined, and very few units are identical.
Early reactors have steel pressure vessels, while later units ([[Oldbury nuclear power station|Oldbury]] and [[Wylfa]]) are of reinforced concrete; some are cylindrical in design, but most are spherical.
Working pressure varies from 6.9 to 19.35 [[Bar (unit)|bar]] for the steel pressure vessels, and the two reinforced concrete designs operated at 24.8 and 27 bar.
No British construction company at the time was large enough to build all the power stations,
so various competing consortia were involved, adding to the differences between the stations.
[[On-load refuelling]] was an economically essential part of the design, to maximise power station availability by eliminating refuelling downtime. This was particularly important for Magnox as the unenriched fuel had a low [[burnup]], requiring more frequent changes of fuel than most [[enriched uranium]] reactors.
==Safety==
The Magnox reactors have a considerable degree of inherent safety because of their sturdy design, low power density, and gas coolant. As such, they do not require or possess [[secondary containment]] features. [[Loss of coolant]] accidents—considered in the design—would not cause large-scale fuel failure as the Magnox cladding would retain the bulk of the radioactive material, assuming the reactor was rapidly shutdown (a [[SCRAM]]). As the coolant is already a gas, explosive pressure buildup from boiling is not a risk, as happened in the catastrophic [[steam explosion]] at the [[Chernobyl accident]].
In the older steel pressure vessel design, boilers and gas ducting are outside the concrete biological shield. Consequently this design emits a significant amount of direct [[gamma radiation|gamma]] and [[neutron radiation|neutron]] radiation, termed direct "shine", from the reactors. For example the most exposed members of the public living near [[Dungeness Power Station|Dungeness]] Magnox reactor in 2002<ref>http://www.bnfl.com/dischargesreport2002/121.htm#p139</ref> received 0.56 [[Sievert|mSv]], over half the [[International Commission on Radiological Protection]] recommended maximum radiation dose limit for the public, from direct "shine" alone. The doses from the [[Oldbury nuclear power station|Oldbury]] and [[Wylfa]] reactors, which have concrete pressure vessels which encapsulate the complete gas circuit, are much lower.
==Reactors in use==
[[Image:Sizewell_A.jpg|thumb|right|300px|[[Sizewell nuclear power stations#Sizewell A|Sizewell A]] Magnox nuclear power station]]
In all, 11 power stations totalling 26 units were built in the [[United Kingdom|UK]] where the design originated. In addition, one was exported to [[Japan]] and another to [[Italy]]. [[North Korea]] also developed their own Magnox reactors based on the UK design, which was made public at an [[Atoms for Peace]] conference.
The first Magnox power station, [[Sellafield|Calder Hall]], was the world's first commercial nuclear power station. First connection to the grid was on [[27 August]] [[1956]], and the plant was officially opened by [[Elizabeth II of the United Kingdom|Queen Elizabeth II]] on [[17 October]] [[1956]].<ref>http://www.bnfl.com/index.aspx?page=413</ref> When the station closed on [[31 March]] [[2003]], the first reactor had been in use for nearly 47 years.<ref>http://www.guardian.co.uk/nuclear/article/0,2763,918724,00.html</ref>
However the first two stations (Calder Hall and [[Chapelcross nuclear power station|Chapelcross]]) were originally owned by the [[UKAEA]] and primarily used in their early life to produce [[weapons-grade]] [[plutonium]], with two fuel loads per year.<ref>http://www.nautilus.org/archives/pub/ftp/napsnet/papers/hayes1193.txt</ref> From 1964 they were mainly used on commercial fuel cycles, however it was not until April 1995 that the UK Government announced that all production of plutonium for weapons purposes had ceased.<ref>http://www.mod.uk/publications/nuclear_weapons/accounting.htm</ref>
The later and larger units were owned by [[CEGB]] and operated on commercial fuel cycles.
In operation it was found that there was significant oxidation of mild steel components by the high temperature carbon dioxide coolant, requiring a reduction in operating temperature and power output. For example the [[Latina, Italy|Latina]] reactor was derated in 1969 by 24%, from 210 MWe to 160 MWe, by the reduction of operating temperature from 390 to 360 [[Celsius]].
As of 2007, just two Magnox power stations remain in operation; [[Oldbury nuclear power station|Oldbury]] will close in 2008 and [[Wylfa]] in 2010.
==Magnox==
{{main|magnox (alloy)}}
'''Magnox''' is also the name of an [[alloy]]—mainly of [[magnesium]] with small amounts of [[aluminium]] and other metals—used in cladding unenriched [[uranium]] metal fuel with a non-oxidising covering to contain fission products.
'''Magnox''' is short for '''Mag'''nesium '''n'''on-'''ox'''idising.
This material has the advantage of a low [[neutron]] capture cross-section, but has two major disadvantages:
*It limits the maximum temperature, and hence the thermal efficiency, of the plant.
*It reacts with water, preventing long-term storage of spent fuel under water.
Magnox fuel incorporated cooling fins to provide maximum heat transfer despite low operating temperatures, making it expensive to produce. While the use of uranium metal rather than oxide made reprocessing more straightforward and therefore cheaper, the need to reprocess fuel a short time after removal from the reactor meant that the fission product hazard was severe. Expensive remote handling facilities were required to address this danger.
The term '''magnox''' may also loosely refer to:
*Three [[North Korea]]n reactors, all based on the declassified blueprints of the Calder Hall Magnox reactors:
**A small 5 [[MWe]] experimental reactor at [[Yongbyon Nuclear Scientific Research Center|Yongbyon]], operated from 1986 to 1994, and restarted in 2003. Plutonium from this reactor's spent fuel has been used in the [[North Korea nuclear weapons program]].
**A 50 MWe reactor, also at Yongbyon, whose construction commenced in 1985 but was never finished in accord with the [[Agreed Framework|1994 U.S.-North Korea Agreed Framework]].
**A 200 MWe reactor at [[Taechon]], construction of which also halted in 1994.
*Nine [[UNGG]] power reactors built in [[France]], all now shut down. These were carbon dioxide-cooled, graphite reactors with natural uranium metal fuel, very similar in design and purpose to the British Magnox reactors except that the fuel cladding was [[magnesium]]-[[zirconium]] alloy.
The accepted term for all of these first-generation, carbon dioxide-cooled, graphite-moderated reactors, including the Magnox and UNGG, is '''GCR''' for '''[[Gas Cooled Reactor]]'''.
The Magnox was replaced in the British power station program by the [[Advanced gas-cooled reactor]] or AGR, which was derived from it. A key feature of the AGR was the replacement of magnox cladding to allow higher temperatures and greater thermal efficiency. Stainless steel cladding was adopted after many other alloys had been tried and rejected.
==Decommissioning==
The [[Nuclear Decommissioning Authority]] (NDA) is responsible for the decommissioning of the UK Magnox power plants, at an estimated cost of £12.6 billion. There is currently debate about whether a 25 or 100 year decommissioning strategy should be adopted. After 80 years short-lifetime radioactive material in the defueled core would have decayed to the point that human access to the reactor structure would be possible, easing dismantling work. A shorter decommissioning strategy would require a fully robotic core dismantling technique.<ref>http://www.sitestakeholdergroups.org.uk/oldbury/upload/oldbury_and_berkeley_joint_meeting_minutes_01_nov_06.pdf#page=7</ref>
In addition the [[BNFL]] [[Sellafield]] site which, amongst other activities, [[nuclear reprocessing|reprocessed]] spent Magnox fuel in its [[B205]] plant, has an estimated decommissioning cost of £31.5 billion. Magnox fuel is produced at [[Springfields]] near [[Preston]]; estimated decommissioning cost is £371 million. The total cost of decommissioning Magnox activities is likely to exceed £20 billion, averaging about £2 billion per productive reactor site.
Calder Hall was opened in 1956 as the world’s first commercial nuclear power station, and is a significant part of the UK’s industrial heritage. The NDA is considering whether to preserve Calder Hall Reactor 1 as a museum site.
All the UK's Magnox Reactor Sites (apart from Calder Hall) are operated by Magnox Electric, on behalf of the Nuclear Decommissioning Authority. In 2007, American nuclear fuel cycle service provider Energy''Solutions'' acquired Reactor Sites Management Company (RSMC) from British Nuclear Fuels.
==List of Magnox reactors in the UK==
*[[Sellafield#Calder_Hall_nuclear_power_station|Calder Hall]] near [[Whitehaven]], [[Cumbria]] - 4 units 50 MWe each, first grid connection 1956, shut down 2003 ({{gbmappingsmall|NY025042}})
*[[Chapelcross nuclear power station|Chapelcross]] near [[Annan, Dumfries and Galloway|Annan]], [[Dumfriesshire]], 4 units 50 MWe each, first grid connection 1959, shut down 2003 ({{gbmappingsmall|NY215696}})
*[[Berkeley nuclear power station|Berkeley]] in [[Gloucestershire]], 2 units 138 MWe each, first grid connection 1962, shut down 1989. ({{gbmappingsmall|ST659994}})
*[[Bradwell Power Station|Bradwell]] near [[Southminster]], [[Essex]], 2 units 121 MWe each, first grid connection 1962, shut down 2002 ({{gbmappingsmall|TM001087}})
*[[Hunterston A nuclear power station|Hunterston "A"]] between [[West Kilbride]] and [[Fairlie, North Ayrshire|Fairlie]], [[North Ayrshire]] 2 reactors initially rated at 180 MWe each, later downrated to 150 MWe each, feeding 6 turbo-alternators capable of up to 60MWe each. First grid connection 1964, Reactor 2 shut down 31 December 1989; Reactor 1 shut down 31 March 1990 ({{gbmappingsmall|NS183513}})
*[[Hinkley Point A nuclear power station|Hinkley Point "A"]] near [[Bridgwater]], [[Somerset]], 2 units 235 MWe each, first grid connection 1965, shut down 1999 ({{gbmappingsmall|TR330623}})
*[[Trawsfynydd]] in [[Gwynedd]], 2 units 195 MWe each, first grid connection 1965, shut down 1991 ({{gbmappingsmall|SH690381}})
*[[Dungeness Power Station|Dungeness "A"]] in [[Kent]], 2 units 219 MWe each, first grid connection 1966, shut down 2006 ({{gbmappingsmall|TR074170}})
*[[Sizewell nuclear power stations#Sizewell A|Sizewell "A"]] near [[Leiston]], [[Suffolk]], 2 units 210 MWe each, first grid connection 1966, shut down December 2006 ({{gbmappingsmall|TM472634}})
*[[Oldbury nuclear power station|Oldbury]] near [[Thornbury, South Gloucestershire]], 2 units 217 MWe each, first grid connection 1968, planned to be shut down in 2008. ({{gbmappingsmall|ST606945}})
*[[Wylfa]] on [[Anglesey]], 2 units 490 MWe each, first grid connection 1971, planned shut down of 2010 ({{gbmappingsmall|SH350937}})
==Magnox reactors exported from the UK==
*[[Latina Nuclear Power Plant|Latina]], [[Italy]], 1 unit 160 MWe, first grid connection 1963, shut down 1987 following [[Italian nuclear power referendum, 1987|Italian referendum on nuclear power]]
*[[Tokai, Ibaraki]], [[Japan]], 1 unit 166 MWe, first grid connection 1966, shut down 1998
==See also==
*[[Nuclear power in the United Kingdom]]
*[[UNGG reactor|UNGG]], the similar class of reactors built in [[France]]
*[[List of nuclear reactors]]
*[[Edge of Darkness]], 1985 British television drama about the nuclear industry, which went by the working title "Magnox".
*[[Yongbyon Nuclear Scientific Research Center]], location of the North Korean Magnox-type reactor.
{{Nuclear Technology}}
==References==
{{Reflist}}
==External links==
*[http://www.magnoxelectric.com/ Magnox Electric],
*[http://www.energysolutions.com/ Energy''Solutions''],
*[http://www.nuclearsites.co.uk Nuclear Sites Stakeholder Information] - Overview of each Magnox power station, provided by British Nuclear Group
*[http://www.hse.gov.uk/nuclear/magnox.pdf Magnox Safety Reviews], September 2000, [[Health and Safety Executive|HSE]] Nuclear Installations Inspectorate
*[http://www.hse.gov.uk/nuclear/magdecom.pdf Magnox Electric plc’s strategy for decommissioning its nuclear licensed sites], February 2002, [[Health and Safety Executive|HSE]] Nuclear Installations Inspectorate
*[http://www.iaea.org/inis/aws/htgr/abstracts/abst_29059903.html The decommissioning of commercial magnox gas cooled reactor power stations in the United Kingdom], G. Holt, Magnox Electric, IAEA meeting paper, 8-10 September 1997
*[http://www.defra.gov.uk/rwmac/reports/reprocess/16.htm Disposal of Magnox spent fuel] - [[BNFL]]
*[http://www.iaea.org/inis/aws/htgr/abstracts_c/abst_iwggcr19_17.html Operating experience with the Latina Magnox reactor], 21-23 September 1988, Ente Nazionale per l'Energia Elettrica
*[http://www.telltony.greenpeace.org.uk/MultimediaFiles/Live/FullReport/3244.pdf Review of ageing processes and their influence on Safety and Performance at Wylfa Nuclear Power Station], [[John Large]], 14 March 2001 - includes detailed diagrams
*[http://www.atomicinsights.com/jan96/Magnox.html Magnox Fuel Element Design] - Atomic Energy Insights
*[http://www.neimagazine.com/story.asp?sectionCode=132&storyCode=2032396 Sellafield Magnox cooling ponds cleanup job commences] - Nuclear Engineering International
*[http://www.neimagazine.com/story.asp?storyCode=2038060 A ponderous hazard] - Nuclear Engineering International
*[http://magnox.info British Nuclear Group image asset library] - A large collection of interior and exterior photographs of all the Magnox power stations in the UK.
[[Category:Nuclear power reactor types]]
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